Cerebellar long-term depression (LTD) is a model system for neuronal information storage that has an absolute requirement for activation of protein kinase C (PKC). It has been claimed to underlie several forms of cerebellar motor learning. Previous studies using various knockout mice (mGluR1, GluRdelta2, glial fibrillary acidic protein) have supported this claim; however, this work has suffered from the limitations that the knockout technique lacks anatomical specificity and that functional compensation can occur via similar gene family members. To overcome these limitations, a transgenic mouse (called L7-PKCI) has been produced in which the pseudosubstrate PKC inhibitor, PKC[19-31], was selectively expressed in Purkinje cells under the control of the pcp-2(L7) gene promoter. Cultured Purkinje cells prepared from heterozygous or homozygous L7-PKCI embryos showed a complete blockade of LTD induction. In addition, the compensatory eye movements of L7-PKCI mice were recorded during vestibular and visual stimulation. Whereas the absolute gain, phase, and latency values of the vestibulo-ocular reflex and optokinetic reflex of the L7-PKCI mice were normal, their ability to adapt their vestibulo-ocular reflex gain during visuo-vestibular training was absent. These data strongly support the hypothesis that activation of PKC in the Purkinje cell is necessary for cerebellar LTD induction, and that cerebellar LTD is required for a particular form of motor learning, adaptation of the vestibulo-ocular reflex.

A genomic clone encoding the Purkinje cell-specific L7 protein has been isolated and utilized to drive the expression of beta-galactosidase in mice. Three independent transgenic lines, germ line transformed with an L7-beta-galactosidase fusion gene, exhibit beta-galactosidase expression in both cerebellar Purkinje cells and retinal bipolar neurons. This distribution is the same as that previously determined for the L7 protein by immunohistochemistry. The transgenic murine lines can be used to obtain populations of marked Purkinje and bipolar neurons. Similar L7 promoter constructs can be used to express other foreign genes specifically in these two classes of neurons.

The mouse cerebellar cortex is subdivided by an elaborate array of parasagittal and transverse boundaries. The relationship between these two orthogonal patterns of compartmentation is understood poorly. We have combined the use of adult and perinatal molecular markers of compartmentation—zebrin II, calbindin, and an L7/pcp‐2‐lacZ transgene—to resolve some of these issues. Our results indicate that the adult cerebellar vermis is divided along the rostrocaudal axis by three transverse boundaries: through the rostral face of lobule VI, in the caudal half of lobule VII, and across the posterolateral fissure between lobules IX and X. These three boundaries subdivide the vermis into four transverse zones: the anterior zone (lobules I–V), the central zone (lobules VI–VII), the posterior zone (lobules VIII–IX), and the nodular zone (lobule X). The same zones and boundaries also can be identified in the newborn cerebellum. The parasagittal organization is different in each zone: a unique combination of Purkinje cell phenotypes is found in each transverse zone both in the neonate and the adult, and different zones have distinct developmental time tables. Furthermore, the parasagittal bands of Purkinje cells revealed in the adult cerebellar cortex by using antizebrin II immunocytochemistry are discontinuous across the transverse boundaries. These data suggest that the transverse zones of the vermis form first during development and that parasagittal compartmentation develops independently in each transverse zone. J. Comp. Neurol. 412:95–111, 1999. © 1999 Wiley‐Liss, Inc.

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